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A strobiology. Announcements. Homework #4 due on Thursday Quiz #2 on Thursday Closed book, closed note, no electronic devices Chapters 9, 10, and 11 Lecture material up through this Thursday. What is astrobiology?. NASA Astrobiology Program seeks to answer: How does life begin and evolve?

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announcements
Announcements
  • Homework #4 due on Thursday
  • Quiz #2 on Thursday
    • Closed book, closed note, no electronic devices
    • Chapters 9, 10, and 11
    • Lecture material up through this Thursday

Astrobiology

3/20/12

what is astrobiology
What is astrobiology?
  • NASA Astrobiology Program seeks to answer:
    • How does life begin and evolve?
    • Does live exist elsewhere in the universe? How can we detect it?
    • What is the future of life on Earth and Beyond?

Astrobiology

3/20/12

properties of life
Properties of life

Astrobiology

3/20/12

properties of life1
Properties of life

Order, organization (organs, tissues, cells, molecules, atoms)

Energy utilization and production (metabolism)

Maintenance of internal constancy (homeostasis)

Reproduction, growth, and development

Response to the environment (react to stimuli)

Evolutionary adaptation (slow change)

Astrobiology

3/20/12

is it alive
Is it alive?

Astrobiology

3/20/12

is it alive1
Is it alive?

Astrobiology

3/20/12

is it alive2
Is it alive?

Astrobiology

3/20/12

is it alive3
Is it alive?

Astrobiology

3/20/12

is it alive4
Is it alive?

Astrobiology

3/20/12

is it alive5
Is it alive?

Which is alive?

Astrobiology

3/20/12

definition of life
Definition of life
  • “A system capable of evolution by natural selection”

(Carl Sagan, 1970)

  • “A self-sustaining chemical system capable of undergoing Darwinian evolution”

(NASA’s definition)

Astrobiology

3/20/12

necessities of life
Necessities of life
  • To search for life we need to know the requirements for life
  • These are based on our only reference system: Earth
  • Life requires:
      • Organic molecules: Carbon, hydrogen, oxygen, nitrogen, phosphorus, sulfur (CHONPS)
      • A source of energy
      • The presence of a solvent: liquid water
      • Suitable environmental conditions (for example temperature and pressure)

Astrobiology

3/20/12

origin of life primordial soup theory
Origin of life - Primordial soup theory

Basic building blocks of life combined to form complex organic molecules such as amino acids, proteins, and an early version of RNA in a warm pond or ocean.

Astrobiology

3/20/12

synthesis of small organic molecules atmosphere
Synthesis of small organic molecules – Atmosphere

Miller-Urey Experiment:

(1952)

A spark (analogous to lightning) breaks apart C4H, NH3, and H2O components of the ancient atmosphere and the atoms recombine to form simple organic molecules.

Astrobiology

3/20/12

problems of organic synthesis via miller urey experiment
Problems of organic synthesis via Miller-Urey experiment

The composition of the ancient atmosphere is not well known  might have had less C4H and NH3 than assumed by Miller and Urey

Organic production by spark discharge is not very efficient in a CO2 rich atmosphere

However, if CH4/CO2 < 0.1 very few organics are produced

Astrobiology

3/20/12

synthesis of small organic molecules hydrothermal vents
Synthesis of small organic molecules –Hydrothermal Vents
  • Problems:
    • Only very simple organics are generated
    • Complex organics are unstable at high temperatures

Hydrothermal vents are fissures in a planet’s surface which geothermally heat water

Near hydrothermal vents, silicate rocks, CO2, and H2O combine to form simple organic molecules

Astrobiology

3/20/12

synthesis of small organic molecules extraterrestrial
Synthesis of small organic molecules – Extraterrestrial

Problems:

  • Simple organics only
  • It’s hard to accumulate enough organics in one place

Murchison (1969, Australia)

Meteorites sometimes contain amino acids and other organic molecules

Astrobiology

3/20/12

the dilution problem
The Dilution Problem
  • Earth’s early oceans were probably too dilute in simple organic molecules to form bigger molecules
  • Possible concentration mechanisms
    • Tidal pools (evaporation)
    • Freezing water
    • Mineral catalysts – small organic molecules could have stuck to the mineral surface in an organic film.

Astrobiology

3/20/12

origin of life summary
Origin of life summary

Astrobiology

3/20/12

extremophiles
Extremophiles
  • Organisms that thrive in extreme conditions such as high or low temperature, high pressure, salty water, acidic water, low amounts of water, and/or high radiation environments
  • The earliest living organisms on Earth were extremophiles.
    • The atmosphere had very little oxygen, so there was no protection from UV radiation
    • The oceans were hot and probably acidic because of volcanism

Astrobiology

3/20/12

temperature
Temperature

High temperature – proteins denature, chemical reactions slow down

Pyrolobusfumarii – lives in hydrothermal vents. The upper limit for active growth is 121°C (250°F), but it can survive up to 130°C (266°F).

Astrobiology

3/20/12

temperature1
Temperature

Grylloblatids – ice bugs – body fluids act as antifreeze

Snow algae – cold-tolerant algae grows on snow and ice

Low temperature – water freezes which breaks cell membranes

Current lower limit for active growth is -20°C

Astrobiology

3/20/12

pressure
Pressure

Halomonassalaria

High pressure can make cell membranes relatively impermeable for nutrients

Current upper limit is > 1000 atm (pressure at Earth’s surface is 1 atm)

Astrobiology

3/20/12

salinity
Salinity

Dunaliellasalina– pink micro-algae found in sea salt fields

Proteins are less soluble at high salt concentrations

Astrobiology

3/20/12

acidity ph
Acidity (pH)

Tinto river (Andalusia Spain) – pH ≈ 2 contains aerobic bacteria

  • pH = -log[H+] The amount of H+ measures the acidity of a solution (pH = 0 is most acidic; pH = 14 is most basic)
  • Current limits:
    • pH ≈ 0 Ferroplasma

acidarnamus(acid

mine drainage, CA)

    • pH ≈ 13 Plectonema

(soda lakes)

Astrobiology

3/20/12

water availability
Water availability
  • Tardigrades – “water bears”
  • ~1mm
  • Anydrobiosis - their body desiccates and waits for moisture to return
  • While in anydrobiosis they can survive
    • -272.95°C for 20 hours
    • -200°C for 20 months
    • +120°C (above boiling)
    • Pressures of 1,000 atm
    • Pure vacuum

Extreme desiccation can cause irreversible phase changes to lipids, proteins, and nucleic acids

Astrobiology

3/20/12

radiation
Radiation
  • DeinococcusRadiodurans
  • Can survive cold, dehydration, vacuum, and acid
  • Can survive 1000 times radiation amounts that would kill humans
  • Carries between 3 and 10 copies of its DNA, so it can make repairs after damage from radiation or dehydration

Radiation damages DNA

Astrobiology

3/20/12

endoliths
Endoliths

Bacillus infernus– lives up to 3 km beneath Earth’s surface.

Photo courtesy of US Dept. Energy

Anaerobic organisms that survive by eating Fe, K, or S (rock) and live between the mineral grains of a rock

Astrobiology

3/20/12

looking for life in the solar system
Looking for life in the solar system
  • These ‘extreme’ environments on Earth may be ‘normal’ in other parts of the solar system
  • Life requires:
      • Organic molecules: Carbon, hydrogen, oxygen, nitrogen, phosphorus, sulfur (CHONPS)
      • A source of energy
      • The presence of a solvent: liquid water
      • Suitable environmental conditions (for example temperature and pressure)
  • NASA’s approach is: Follow the water!

Astrobiology

3/20/12

why water
Why water?

H and O are abundant in the universe

It remains liquid over a wide range of temperatures

Usually substances sink when frozen, but water ice floats (underwater life can survive freezing temperatures at the surface)

It’s a polar molecule, so it can dissolve some substances but not cell

membranes

Astrobiology

3/20/12

slide32
Mars

Mars has a similar composition to Earth, but its water is mostly frozen, it has a thin atmosphere, no ozone layer, no magnetic field, and is less geologically active.

It may have been warmer and wetter in the past.

Deep subsurface permafrost could harbor endolith (in rock) communities today.

Astrobiology

3/20/12

slide33
Mars
  • ALH8401, a Martian meteorite, has structures that were briefly considered to be fossilized remains of bacteria-like life forms
  • But all the evidence for

life could be explained

without life too.

Astrobiology

3/20/12

europa
Europa

The subsurface ocean could harbor life, especially if there are hydrothermal vents at the ocean floor.

Astrobiology

3/20/12

europa1
Europa

Cracks in the ice shell open and close periodically due to tidal flexing. Photosynthetic life might be able to live in the cracks.

titan
Titan

Image from the decent of the Huygens probe

Solid ice surface, methane rain and lakes, thick atmosphere. Geology is similar to Earth except for composition.

Organisms could be consuming hydrogen, acetylene, and ethane to produce methane (Cassini/Huygens data is consistent with but does not prove this).

Astrobiology

3/20/12

venus enceladus
Venus? Enceladus?

Venus has stable cloud layers 50 km above the surface with hospitable climates and chemical disequilibrium, so some speculate that microbes could live there.

Enceladus spews water into space with discharge rates similar to Old Faithful geyser in Yellowstone National Park.

Somewhere else?

Astrobiology

3/20/12

outside our solar system extrasolar planets
Outside our solar system – Extrasolar planets

762 extrasolar planets have been discovered as of yesterday, 3/19/12

(http://exoplanet.eu/catalog.php)

More on detection of extrasolar planets and the types of planets that have been found in a few weeks…

Astrobiology

3/20/12

habitable zone
Habitable zone

Minimum and maximum estimates for the extent of the habitable zone in our solar system.

The region around a star where a planet can maintain liquid water on its surface

Changes with time as the star evolves

An atmosphere (greenhouse effect) or geologic activity could warm planet

Salt can lower the freezing point of water

Astrobiology

3/20/12

how can we tell if a planet can support life
How can we tell if a planet can support life?

Look for oxygen

Look for liquid water

Analyze the reflected light from the planet to see if it has an atmosphere

Look for signs of biological activity (methane)

And rule out other explanations!

Astrobiology

3/20/12

the search for life on earth
The search for life on Earth
  • Simultaneous presence of O2 or O3 and a reduced gas (CH4 or N2O) is the best evidence for life
  • The Galileo mission observed Earth during a fly by
  • It detected oxygen and methane
  • We could detect life on Earth!
  • We are beginning to try to do this for extrasolar planets

Astrobiology

3/20/12

slide42
SETI

Search for ExtraTerrestrial Intelligence

Started in early 1960s (institute was founded in 1984)

Looks for non-random electromagnetic signals transmitted by intelligent civilizations

SETI@home: volunteer use of internet connected computers to analyzed radio-telescope data

It has not found any other civilizations yet

Astrobiology

3/20/12

the drake equation
The Drake equation

What is the probability that we are not alone?

The Drake equation attempts to estimate the number of civilizations capable of interstellar communication:

N = Rs× fp× np× fL× fi× fc× Lc

Rs= rate of sun-like star formation (best known factor: 1-10)

fp = fraction of stars with planets (0.2-0.5)

np= number of habitable planets per star (0.1- 5)

fL = fraction of habitable planets with life (0.0001-1)

fi = fraction of planets where intelligent life evolves (0.001-1)

fc= fraction of intelligent civilizations capable of interstellar communication (0.01-1)

Lc = average lifetime of those civilizations (60 yrs – ???)

Astrobiology

3/20/12